Glass fiber sizing compositions and methods of using same

ABSTRACT

The present invention is directed to sizing compositions for use on glass fibers which are used to reinforce lamination resins used in the formation of glass laminates. The sizing compositions contain a low molecular weight, polymer latex prepared by polymerizing at least one monomer(s) selected from the group consisting of acrylic acid, methacrylic acid, C 1  -C 18  alkyl esters of acrylic acid, C 1  -C 18  alkyl esters of methacrylic acid, glycidyl acrylate, glycidyl methacrylate, C 1  -C 4  hydroxyalkyl esters of acrylic acid, C 1  -C 4  hydroxyalkyl esters of methacrylic acid, vinyl esters of saturated aliphatic monocarboxylic acids containing up to 10 carbon atoms, (meth)acrylamide and their N-substituted derivatives, vinyl ethers, N-vinyl lactams, halogenated vinyl compounds, alkyl vinyl ketones, (meth)allyl ester of saturated aliphatic monocarboxylic acids, vinyl compounds such as vinyl pyrrole, olefins, diesters of itaconic, maleic and/or fumaric acid, and styrene. The polymers have a molecular weight effective to provide both improved wettability of the glass fibers by the lamination resins and improved clarity of reinforced glass laminates prepared from the sized glass fibers and the lamination resins, when compared to sizing compositions known heretofore. The invention is also directed to glass fibers treated with such compositions, and fiber-reinforced plastics prepared from such treated glass fibers.

FIELD OF THE INVENTION

This invention relates to novel compositions for sizing glass fibers,glass fibers treated with the sizing compositions and fiber-reinforcedplastics prepared from such sized glass fibers.

BACKGROUND OF THE INVENTION

The sizing of glass fibers which are used to reinforce plastic resinmatrices is well known. For instance, U.S. Pat. No. 3,997,306 disclosesglass fiber size which contains a phenolic epoxy resin, the reactionproduct of the partial ester of a polycarboxylic acid containing one ormore unesterified carboxyl groups with a compound containing more thanone epoxy group, an amino silane coupling agent, a methacryloxy alkyltrialkoxy silane, and a non-ionic surface active agent.

U.S. Pat. No. 4,126,729 discloses gun roving glass fibers coated with anaqueous-based size comprising an epoxidized polyvinyl acetate copolymerin combination with a vinyl acetate-ethylene copolymer and a vinylacetate copolymer.

U.S. Pat. No. 4,457,970 discloses treated glass fiber strands withimproved processing characteristics. The treated glass fiber strandshave on the glass fibers comprising the glass fiber strand an aqueoustreating composition or a dried residue thereof. The treatingcomposition has a vinyl-containing coupling agent, an epoxidizedthermoplastic polymer or copolymer, an organo-reactable silane couplingagent in an unhydrolyzed and/or partially hydrolyzed condition or aninteraction product of the epoxidized polymer or copolymer andorgano-reactable silane coupling agent, and a glass fiber lubricant.U.S. Pat. No. 4,789,593 discloses glass fibers treated with an aqueouschemical treating composition having a polar thermoplastic film-formingpolymer, coupling agent and lubricant. The aqueous emulsion of thethermoplastic film forming polymer has an average amount of aliphaticunsaturation of less than around 1.5 aliphatic double bonds/mole ofpolymer and has a ratio of aliphatic unsaturation to aromaticunsaturation not to exceed 0.1.

It is desirable to develop sizing compositions which provide betterwettability of glass fibers by plastic resins than sizing compositionsnoted herein above. It is further desirable to develop sizingcompositions which, when applied to glass fibers or strands which areused to reinforce plastic resin matrices, yield fiber-reinforcedplastics (FRP) produced from the reinforced plastic resin matrices whichhave better clarity than laminates produced from polymeric matricesreinforced with glass fibers or strands treated with sizing compositionsknown heretofore.

SUMMARY OF THE INVENTION

The present invention is directed to sizing compositions for use onglass fibers which are used to reinforce plastic resins used in theformation of fiber-reinforced plastics (FRP). The sizing compositionscomprise a low molecular weight polymer prepared by polymerizing atleast one monomer(s) selected from the group consisting of acrylic acid,methacrylic acid, C₁ -C₁₈ alkyl esters of acrylic acid, C₁ -C₁₈ alkylesters of methacrylic acid, glycidyl acrylate, glycidyl methacrylate, C₁-C₄ hydroxyalkyl esters of acrylic acid, C₁ -C₄ hydroxyalkyl esters ofmethacrylic acid, vinyl esters of saturated aliphatic monocarboxylicacids containing up to 10 carbon atoms, (meth)acrylamide and theirN-substituted derivatives, vinyl ethers, N-vinyl lactams, halogenatedvinyl compounds, alkyl vinyl ketones, (meth)allyl ester of saturatedaliphatic monocarboxylic acids, vinyl compounds such as vinyl pyrrole,olefins, diesters of iraconic, maleic and/or fumaric acid, and styrene.The polymers have a molecular weight effective to provide both improvedwettability of the glass fibers by the plastic resins and improvedclarity of FRPs prepared from the sized glass fibers and the plasticresins, when compared to sizing compositions known heretofore. Theinvention is also directed to glass fibers treated with suchcompositions, and FRPs prepared from such treated glass fibers.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to sizing compositions which are used totreat glass fibers which are subsequently used to reinforce plasticresinsin the preparation of fiber-reinforced plastics (FRPs). As usedherein, glass fibers collectively refers to continuous glass fiberfilaments formed by the attenuation of a stream, or streams, of moltenglass, to strands formed when continuous glass fiber filaments aregathered togetherin forming and to glass rovings formed from the glassstrands. As used herein, plastic resin refers to thermoplastic orthermosetting resins typically used to prepare FRPs. Examples of suchplastic resins include, without limitation, styrenated polyester andvinyl ester resins. An exemplary unsaturated polyester resin dissolvedin styrene and methyl methacrylate is MR 17090, available from AristechChemical Corporation, Pittsburgh, Pa. As used herein, FRP refers toplastic resin matrices whichhave been reinforced with glass fibers whichhave been treated with glass-size compositions.

Such sizing compositions typically comprise a thermoplastic,film-forming resin used as a forming binder for the glass fibers used inpreparation ofthe FRPs. In the present invention, the resin compriseslow molecular weight polymers, preferably prepared by emulsionpolymerization of at least one monomer(s) selected from the groupconsisting of acrylic acid, methacrylic acid, C₁ -C₁₈ alkyl esters ofacrylic acid, C₁ -C₁₈ alkyl esters of methacrylic acid, glycidylacrylate, glycidyl methacrylate, C₁ -C₄ hydroxyalkyl esters of acrylicacid, C₁ -C₄ hydroxyalkyl esters of methacrylic acid, vinyl esters ofsaturated aliphatic monocarboxylic acids containing up to 10 carbonatoms such as vinyl acetate, (meth)acrylamide and their N-substitutedderivatives such as N-mono and N-dimethyl, -ethyl, -propyl, and -butylacrylamide, vinyl ethers such as butyl vinyl ether, N-vinyl lactams suchas N-vinyl pyrrolidinone, halogenated vinyl compounds such as vinylchloride and vinylidene chloride, alkyl vinyl ketones such as methyl orethyl vinyl ketone, (meth)allyl ester of saturated aliphaticmonocarboxylic acids such as allyl and methallyl acetates, propionatesandvalerates, vinyl compounds such as vinyl pyrrole, olefins such asethylene,diesters such as dimethyl, diethyl, dipropyl, dibutyl,diphenyl, dibenzyl and di(phenylethyl) itaconate, maleate and/orfumarate and styrene. Preferably, the monomer(s) is selected from thegroup consisting of ethyl acrylate, butyl acrylate, methyl methacrylate,glycidyl methacrylate, hydroxypropyl acrylate, vinyl acetate andstyrene.

In certain preferred embodiments, the polymer will comprise the emulsionpolymerization product of a major proportion of at least one acrylicmonomer(s) selected from the group consisting of C₁ -C₁₈ alkyl esters ofacrylic or methacrylic acid, preferably a combination of two or more C₁-C₄ alkyl esters of acrylic and/or methacrylic acid. In suchembodiments, the C₁ -C₁₈ alkyl ester monomer(s) may be copolymerizedwith copolymerizable monomer(s) selected from the group consisting ofacrylic acid, methacrylic acid, glycidyl acrylate, glycidylmethacrylate, C₁ -C₄ hydroxyalkyl esters of acrylic acid, C₁ -C₄hydroxyalkyl esters of methacrylic acid, vinyl acetate and styrene.

In other preferred embodiments, the polymers will comprise the emulsionpolymerization product of a major proportion of a vinyl ester monomer,such as vinyl acetate. Such vinyl ester monomers may be copolymerizedwithother copolymerizable monomer(s) selected from the group consistingof acrylic acid, methacrylic acid, C₁ -C₁₈ alkyl esters of acrylic acid,C₁ -C₁₈ alkyl esters of methacrylic acid, glycidyl acrylate, glycidylmethacrylate, C₁ -C₄ hydroxyalkyl esters of acrylic acid and C₁ -C₄hydroxyalkyl esters of methacrylic acid.

In still other embodiments, the polymers may consist of vinyl acetatehomopolymers or interpolymers of one or more monomer(s) selected fromthe group consisting of C₁ -C₁₈ alkyl esters of acrylic and methacrylicacid monomers.

The polymers utilized in the sizing compositions will have a molecularweight which is effective to provide both improved wettability of theglass fibers by the plastic resins and improved clarity of FRPs preparedfrom glass fibers which have been treated with the inventive sizingcompositions, compared to glass fibers which have been treated withsizingcompositions known heretofore and FRPs prepared therefrom.Preferably, the polymers will have a weight average molecular weight ofno more than about55,000, as determined by Gel PermeationChromotography.

As one skilled in the art will appreciate, molecular weightdeterminations are typically measured relative to some standard. As oneskilled in the art also will appreciate, intrinsic viscosity is oneproperty of polymers which is proportional to the molecular weight,number average or weight average. Therefore, intrinsic viscosity is usedherein to define the weight average molecular weight range of thepolymers utilized in the sizing compositions of the present invention.It is preferred that the polymers have an intrinsic viscosity of lessthan about 0.4 dL/g. It is more preferred that the intrinsic viscosityof the polymers is less than about 0.35 dL/g.

The polymers utilized in the sizing compositions must be capable offormingnon-tacky films on the glass fibers under conditions normallyencountered during the sizing process. Tacky films may build-up onequipment used in processing the treated glass fibers, such as choppers,rollers and the like, which is undesirable. Preferably, the polymerswill form non-tacky films under ambient conditions, i.e., roomtemperature. Accordingly, the glass transition (Tg) of the polymers willbe effective to form such non-tacky films under such noted conditions.The polymers will have a Tg of from about -10° C. to about 70° C.,preferably from about -10° C. to about 40° C., more preferably fromabout 5° C. to about 30° C.

The polymers utilized in the sizing compositions may be prepared viasolution polymerization methods known to those skilled in the art.Preferably, the polymers are prepared via emulsion polymerizationmethods known to those skilled in the art. The monomers or comonomersare dispersed into water and surfactant with agitation sufficient toemulsify the mixture. The aqueous medium may also contain a free radicalpolymerization catalyst or other ingredients that are known andconventionally employed in the art as emulsion polymerization aids.

Suitable free radical polymerization catalysts are the catalysts knownto promote emulsion polymerization and include water-soluble oxidizingagents, such as organic peroxides, inorganic oxidating agents and thosecatalysts that are activated in the water phase by a water-solublereducing agent. Such catalysts are employed in a catalytic amountsufficient to cause polymerization.

Suitable emulsifying agents include anionic, cationic and nonionicemulsifiers customarily used in emulsion polymerization. Usually, one ormore nonionic emulsifier(s) is utilized. Representative nonionicemulsifiers are sorbitan fatty acid esters, ethoxylated sorbitan esters,ethoxylated sorbitol and sorbitol esters, ethoxylated fatty acids,polyethylene glycol fatty acid esters, ethoxylated alcohols, ethoxylatedalkyl phenols, ethoxylated triglycerides, ethoxylated alkanolamines,alkyland glycol esters, glycerol esters and ethylene oxide/propyleneoxide blockcopolymers. The emulsifying agents are employed in amountseffective to achieve adequate latex stability and to provide desiredparticle size and particle size distribution.

Other ingredients known in the art to be useful for various specificpurposes in emulsion polymerization, such as acids, salts, chaintransfer agents, pH buffers and chelating agents, can also be employedin the preparation of the polymer.

The manner of combining the polymerization ingredients can be by variousknown monomer feed methods, such as continuous monomer addition,incremental monomer addition, or addition in a single charge of theentireamount of monomers. The entire amount of the aqueous medium withpolymerization additives can be present in the polymerization vesselbefore introduction of the monomer or, alternatively, the aqueousmedium, or a portion of it, can be added continuously or incrementallyduring the course of polymerization.

Polymerization is initiated by heating the emulsified mixture withcontinued agitation to a temperature usually between about 30°-100° C.,preferably between 50°-90° C. Polymerization is continued by maintainingthe emulsified mixture at the selected temperature until conversion ofthe monomer or monomers to polymer has been substantially completed.Following polymerization, the solids content of the resulting emulsionpolymer can be adjusted to the level desired by the addition of water orby removal of water by distillation.

While not intending to be limited by the following, clarity of the FRPgenerally is a function of the solubility of the sizing composition intheplastic resin. A FRP with improved clarity will contain less "whiteglass";that is, the treated glass fibers will exhibit less gleam orglinting when subjectively observed. Therefore, it is desirable that theglass fibers bewetted completely by the plastic resin such that thefibers comprise a uniform residue of the sizing composition in order toproduce less white glass and higher clarity. As is inferred by the term,wettability relates to the ease with which the plastic resin isdistributed thoroughly upon the surface of the glass fibers. The greaterthe rate at which the fibers are wetted completely by the plastic resin,the better.

The sizing compositions will contain a major proportion of water,preferably greater than 50 weight percent. More preferably, the sizingcompositions will contain greater than about 75 weight percent of water.The sizing compositions can contain from about 0.2 to about 2.0 weightpercent of the polymers, based on the total weight of the sizingcomposition, preferably between about 0.5 to about 1.0 weight percent ofthe polymers.

The sizing compositions also may contain from about 0.01 to about 0.5weight percent of a silane coupling agent, based on the total weight ofthe sizing composition, preferably from about 0.1 to about 0.5 weightpercent of the coupling agent. Any suitable silane coupling agent, suchasgamma-methacryloxypropyltrimethoxysilane, can be employed. Anexemplary silane coupling agent is available from Union Carbide,Danbury, Conn., under the tradename Silane A-174. Other exemplarycoupling agents include vinyltrichlorosilane, vinyltriethoxysilane,vinyltriacetoxysilane and vinyltrimethoxysilane, all available fromUnion Carbide.

The sizing compositions also may contain from about 0.05 to about 1.0weight percent of a lubricant suitable for use in such sizingcompositions, based on the total weight of the sizing composition,preferably from about 0.1 to about 0.25 weight percent of the lubricant.An exemplary cationic polyethyleneimine polyamide salt lubricant iscommercially available from Henkel Corporation, Ambler, Pa., under thetradename Emery 6760.

The sizing compositions can contain from about 0.01 to about 0.05 weightpercent of acetic acid, based on the total weight of the sizingcomposition, preferably from about 0.01 to about 0.03 weight percent ofacetic acid. As those skilled in the art will appreciate, thecompositionsfurther may include other materials commonly used in sizingcompositions, such as Werner-type chromium complexes, protectivecolloids, plasticizers,anti-foaming agents, surfactants, and the like.

The sizing compositions may be applied by any methods known to thoseskilled in the art. They may be applied to the glass fiber filaments, toglass fiber strands or to glass fiber rovings. Glass fiber strands areformed when the continuous glass fiber filaments are gathered togetherin forming and typically contain from about 200-1600 filaments. Glassrovingstypically contain from about 40-60 glass strands. Known methodsof application are discussed in U.S. Pat. Nos. 3,997,306, 4,457,970 and4,789,593, all of which are hereby incorporated by reference in theirentirety.

The FRPs may be formed by any method known to those skilled in the art.Such methods are disclosed, for example, in U.S. Pat. Nos. 4,457,970 and4,789,593. Preferably, the sized glass fibers are chopped to a desiredlength and incorporated into the plastic resin. The plastic resin may beany resin which is compatible with the sizing composition to yield thedesired improved wettability and clarity described herein above.Preferredplastic resins are polyester resins, with styrenated polyvinylesters beingparticularly preferred.

The following examples demonstrate certain embodiments of the invention,but are not intended to limit the scope of the invention, the scope ofwhich is only limited by the claims appended hereto.

Preparation of Polymer Latexes

A series of polymer latexes was prepared via emulsion polymerization.ThoseExamples designated "A" are low molecular weight polymers utilizedin the inventive sizing compositions. Those Examples designated "B" arecomparative high molecular weight polymers utilized in comparativesizing compositions.

The monomer compositions are set forth in Table 1. Monomer compositionscontained therein are given as weight percent, based on the total weightof monomer(s).

Sizing Compositions and Application

Sizing compositions were prepared for each polymer according to thefollowing formulation:

    ______________________________________                                        Components           Grams                                                    ______________________________________                                        Polymer Latex (50% Solids)                                                                          80.00                                                   Silane A-174          2.89                                                    Acetic acid           0.20                                                    Emery 6760            1.40                                                    Water                504.30                                                   ______________________________________                                    

The sizing compositions were applied to unsized glass fiber strands at2% solids based on the glass fiber weight. The strand was immersed in abath of the sizing composition and passed through two squeeze rollers toremoveexcess size. The strand was wound onto a tube and allowed to airdry. Afterair drying, the glass was cured at 130° C. for 30 minutes. Theglasswas allowed to condition overnight at 50% relative humidity and 70°F. prior to preparing FRPs.

Lamination Resin

Polyester lamination resins were prepared according to the followingformulation:

    ______________________________________                                        Components           Grams                                                    ______________________________________                                        Resin MR-17090       800.00                                                   Cumene Hydroperoxide (80%)                                                                          5.60                                                    Benzyltrimethylammonium                                                                             1.44                                                    Chloride (50%)                                                                ______________________________________                                    

FRP Preparation

The glass fiber strand was chopped to a length of 2 inches andincorporatedinto the plastic resin according to the following procedureat a level of 20% by weight, based on the total weight of the FRP. Thesized, chopped glass fibers were placed on a flat panel and the plasticresin poured ontothe chopped glass. The glass was worked into the resinwith minimum force. The combination of the treated glass fibers and theplastic resin was covered by a second flat plate and pressed to aconstant thickness. The combination was heated in a force draft oven at80° C. for thirty minutes to effect curing. The cured FRP was removedfrom the oven and allowed to cool to room temperature.

FRP Clarity

The FRPs prepared from the respective high and low molecular weightpolymers were visually evaluated for clarity and the presence of whiteglass. FRPs were rated subjectively as poor or good. Results arepresentedin Table 1.

Wetting Rate Evaluation

Glass fibers were treated with the respective sizing compositions toachieve a 2.5% solids addition by weight to the fibers. Styrenatedpolyester resin was placed in the light path of a photocell and thetransmittance was set to 100%. The sized fibers were placed in thestyrenated polyester resin, thereby causing the transmittance to drop tonear zero initially. As the polymer residue on the glass fiber waswetted and dissolved by the polyester resin, the transmittanceincreased. The light transmittance was plotted as a function of time.The transmittance (% T) was reported at 2 minutes and 4 minutes. Resultsare presented in Table 1.

                                      TABLE 1                                     __________________________________________________________________________         Chemical     Intrinsic                                                                          (% T)                                                                              (% T)                                                                              Clarity                                      Example                                                                            Composition  Viscosity                                                                          2 minutes                                                                          4 minutes                                                                          Rating                                       __________________________________________________________________________    1A   93 VA/1.3 BA/5.7 HPA                                                                       0.20.sup.1                                                                         43   53   Good                                         1B   93 VA/1.3 BA/5.7 HPA                                                                       0.47.sup.1                                                                         39   45   Poor                                         2A   94 VA/6 BA   0.20.sup.1                                                                         47   55   Good                                         2B   94 VA/6 BA   0.80.sup.1                                                                         39   45   Poor                                         3A   98 VA/2 GMA  0.22.sup.1                                                                         44   52   Good                                         3B   98 VA/2 GMA  0.48.sup.1                                                                         37   44   Poor                                         4A   94 VA/6 HPA  0.20.sup.1                                                                         47   55   Good                                         4B   94 VA/6 HPA  0.75.sup.1                                                                         41   47   Poor                                         5A   100 VA       0.27.sup.2                                                                         43   52   Good                                         5B   100 VA       0.96.sup.2                                                                         41   49   Poor                                         6A   36 MMA/62 EA/2 GMA                                                                         0.34.sup.2                                                                         46   54   Good                                         6B   55 MMA/43 EA/2 GMA                                                                         1.30.sup.2                                                                         44   51   Poor                                         7A   57 MMA/43 EA 0.24.sup.2                                                                         51   60   Good                                         7B   37 MMA/63 EA 0.45.sup.2                                                                         49   56   Poor                                         8A   52 STY/45 EA/3 MMA                                                                         0.20.sup.2                                                                         57   66   Good                                         8B   54 STY/43 EA/3 MMA                                                                         0.50.sup.2                                                                         54   62   Poor                                         __________________________________________________________________________     .sup.1 Intrinsic Viscosity in acetone                                         .sup.2 Intrinsic Viscosity in THF/water                                      VA = vinyl acetate                                                            EA = ethyl acrylate                                                           BA = butyl acrylate                                                           HPA = hydroxypropyl acrylate                                                  GMA = glycidyl methacrylate                                                   STY = styrene                                                             

It is noted that Examples 3A, 3B and 6A had weight average molecularweights of 25, 100, 56,400 and 53,400, respectively, as determined bygel permeation chromatography. As the data indicate, in every case, FRPsprepared from glass fibers which have been sized with the compositionsof the present invention (i.e., low molecular weight polymers) haveimproved clarity over FRPs prepared from glass fibers which have beensized with compositions containing high molecular weight polymers.

Furthermore, the rate at which the sized glass fibers are wet by theplastic resin are higher when the inventive size compositions areutilized, when compared to size compositions utilizing high molecularweight polymers.

We claim:
 1. A sizing composition for use on glass fibers which are usedto prepare fiber-reinforced plastics which contain a plastic resin, thesizing composition comprising: a polymer prepared from at least onemonomer(s) selected from the group consisting of acrylic acid,methacrylic acid, C₁ -C₁₈ alkyl esters of acrylic acid, C₁ -C₁₈ alkylesters of methacrylic acid, glycidyl acrylate, glycidyl methacrylate, C₁-C₄ hydroxyalkyl esters of acrylic acid, C₁ -C₄ hydroxyalkyl esters ofmethacrylic acid, vinyl esters of saturated aliphatic monocarboxylicacids containing up to 10 carbon atoms, (meth)acrylamide and theirN-substituted derivatives, vinyl ethers, N-vinyl lactams, halogenatedvinyl compounds, alkyl vinyl ketones, (meth)allyl ester of saturatedaliphatic monocarboxylic acids, vinyl pyrrole, olefins, diesters ofitaconic, maleic and/or fumaric acid, and styrene, the polymer having aweight average molecular weight of not more than 55,000, as determinedby gel permeation chromotography, to provide improved wettability of theglass fibers by the plastic resin and improved clarity of thefiber-reinforced plastics prepared from the sized glass fibers and theplastic resin compared to size compositions which utilize a polymerhaving a weight average molecular weight of greater than 55,000; and aningredient selected from the group consisting of a silane couplingagent, a lubricant suitable for use in the sizing composition and aceticacid.
 2. The composition of claim 1 wherein the polymer comprises theemulsion polymerization product of a major proportion of at least one ofthe acrylic monomer(s) selected from the group consisting of C₁ -C₁₈alkyl esters of acrylic or methacrylic acid.
 3. The composition of claim2 wherein the C₁ -C₁₈ alkyl ester monomer(s) are copolymerized with atleast one copolymerizable monomer(s) selected from the group consistingof acrylic acid, methacrylic acid, glycidyl acrylate, glycidylmethacrylate, C₁ -C₄ hydroxyalkyl esters of acrylic acid, C₁ -C₄hydroxyalkyl esters of methacrylic acid, vinyl acetate and styrene. 4.The composition of claim 1 wherein the polymer comprises the emulsionpolymerization product of a major proportion of the vinyl ester monomer.5. The composition of claim 4 wherein the vinyl ester monomer is vinylacetate and is copolymerized with at least one copolymerizablemonomer(s) selected from the group consisting of acrylic acid,methacrylic acid, C₁ -C₁₈ alkyl esters of acrylic acid, C₁ -C₁₈ alkylesters of methacrylic acid, glycidyl acrylate, glycidyl methacrylate, C₁-C₄ hydroxyalkyl esters of acrylic acid and C₁ -C₄ hydroxyalkyl estersof methacrylic acid.
 6. The composition of claim 1 wherein the polymerconsists of a vinyl acetate homopolymer.
 7. The composition of claim 1wherein the polymer is a copolymer consisting of one or more monomer(s)selected from the group consisting of C₁ -C₁₈ alkyl esters of acrylicand methacrylic acid monomers.
 8. The composition of claim 1 comprisinga major proportion of water.
 9. The composition of claim 8 comprisingfrom about 0.2 to about 2 weight percent of the polymer, based on thetotal weight of the sizing composition.
 10. The composition of claim 9further comprising from about 0.01 to about 0.5 weight percent of asilane coupling agent and from about 0.05 to about 1.0 weight percent ofa lubricant, based on the total weight of the sizing composition. 11.The composition of claim 10 further comprising from about 0.01 to about0.05 weight percent of acetic acid, based on the total weight of thesizing composition.
 12. The composition of claim 1 wherein the plasticresin is selected from the group consisting of vinyl ester andstyrenated polyester resins.
 13. The composition of claim 12 wherein themonomer(s) is selected from the group consisting of ethyl acrylate,butyl acrylate, methyl methacrylate, glycidyl methacrylate,hydroxypropyl acrylate, vinyl acetate and styrene.